**5. Potential of biotechnology to promote sugarcane as a future energy crop**

dependent phosphofructokinase (PFP) is also partially responsible for being cycled between the hexose phosphate and triose phosphate pools. This cycling was downregulated by constitutive expression of untranslatable and antisense forms of *PFP-b* gene. Approximately 70% activity was decreased in young internodal tissues and no activity was observed in mature tissues. Hendrik and Botha [80] reported decrease in sugar yield as the result of decrease in the PFP activity. A significant increase in sucrose content (in more than 50% of the lines) was observed in the immature internodes, but even 30% downregulation of Pyrophosphate dependent phosphofructokinase (PFP) activity did not affect the mature internodes as compared to wild type. Mature internodes of most of the transgenic lines showed higher sucrose accumulation but was not significant. Hence Pyrophosphate dependent phosphofructokinase (PFP) activity in internodal tissues of sugarcane has a positive relation with respiration and is inversely related with sucrose content. In transgenic plants, no significant difference was observed in development and growth of plants both under greenhouse and field conditions. So PFP (pyrophosphate dependent phosphofructokinase) influences the sucrose accumulation ability of biosynthetically active and young culm of sugarcane. Equilibrium of glycolytic intermediates (stored sucrose) is restored when ATP dependent phosphofructokinase and the

Sugarcane culm is an important experimental system to elucidate biochemical and molecular mechanisms involved in sucrose accumulation or carbon partitioning for the application of gene expression studies in this context [81]. Vacuolar targeted expression of sucrose isomerase gene doubled sucrose accumulation in the culm of greenhouse growing plants. Engineered sugarcane plants not only depicted enhanced sucrose transport but also photosynthesis and sink strengths were improved. These results highlighted importance of sugarcane as an energy crop as more carbon source would result in more biofuel production. Higher level of sucrose and accumulation of isomaltulose (a high value sugar) has also been reported in sugarcane [82]. An experimental study was conducted to explore biosynthesis of isomaltulose (IM) through engineering metabolic pathways. Sucrose (α-D- glucopyranosyl 1,2-D- fructofuranose) is converted into isomaltulose (α-D-glucopyranosyl-1,6-D-fructofuranose) by some bacteria. This sucrose is resistant to several microorganisms as is not metabolized by invertases. Easy digestion (likewise glucose and fructose) by humans is another significant advantage of this sweetener. Instead of salivary invertases, intestinal disaccharidase is involved in the digestion of isomaltulose, so its digestion is relatively slow. Anyhow, it is beneficial because it does not affect insulin and blood glucose levels. Owing to be acariogenic, non-hygroscopic, stable and slowly digestible sweetener, it has mounting market. Biosynthesis of isomaltulose (IM) involves a sucrose isomerase (SI) that does not require cofactor and substrate activation [83]. More isomaltulose (IM) is produced in sugarcane culmn when highly efficient sucrose isomerase (SI) is targeted to vacuole. Further, IM (isomaltulose) could be accumulated without any prominent decrease in sucrose content. Sucrose contents appeared to be doubled in selected transgenic lines but further studies would be required for commercial scale application of this trait i.e. patterns of developmental expression, compartmentation and enzyme stability resulting in high isomaltulose (IM) content. Hence, sucrose isomers can be produced in sugarcane by transgenic technology. Isomaltulose was produced either by expressing sucrose isomerase in the apoplast or in the vacuole. Apoplast-targeted expression did not show any significant

PFP activity is sufficient.

128 Sugarcane - Technology and Research

Plant biomass from grasses including sugarcane, can be used as a renewable source of energy by converting their cellulose, hemicellulose and lignin into bioethanol. Plant derived biofuels reduce dependence on fossil fuels and is of great importance in the countries where oil reserves are limited. Engineering plastid genome of sugarcane may prove a great milestone in this regard [86]. Biofuels produced from plant lignocellulosic biomass (second generation biomass) have advantage over first generation biomass in term of CO2 balance and net energy. Another advantage is that they have no competition for supplies with food industries. As a result, production of bioethanol from 2nd generation biomass is more economical. Sugarcane is one of the most economical source of bioethanol all over the world. Brazil is the leading country in this regard and 50% of the country energy needs are fulfilled by sugarcane ethanol [87]. National fuel alcohol program (ProAlcooL) was launched by Brazil. Major aim of this program was to replace usage of gasoline with bioethanol. In Brazil, 6.19 billion gallons (23.4 billion liters) of ethanol was produced from sugarcane whereas 15% of the total electricity was generated from sugarcane bagasse during 2014 [88]. The genetic foundation of current sugarcane breeding program started with interspecific hybrid varieties originated from early breeding activities in West Indies, India (e.g. Co 206, Co 207) and Indonesia (e.g. POJ 2878, POJ 2364). Sugar yield was increased up to 1–2% per annum by sugarcane programs and most of this increase is attributed to genetics. Conventional breeding in sugarcane has certain limits, as a result desired results could not be achieved. *Saccharum* spp. is genetically complex having 2n = 100–130 with intricate genomic makeup evolved through highly successful interspecific hybridization between *Saccharum spontaneum* and *Saccharum officinarum*, which have well been explored to develop commercial varieties. Ming et al. [89] summarized usage of conventional and molecular approaches for the genetic improvement of sugarcane making it world's most efficient crop in terms of conversion of solar energy into chemical energy.

In sugarcane, about two-third of the photosynthetically fixed carbon is stored in the form of cellulose and hemicellulose. Sugarcane mills produce millions of tons of bagasse annually in addition to the leaves which are left behind in the field. Sugarcane bagasse is an excellent 2nd generation source for production of ethanol and bioelectricity [90]. High cost of enzymes limit the conversion of hemicellulose and cellulose into cellulosic ethanol. Production cost of enzymes can be decreased by the overexpression of cellulolytic enzymes in GM (genetically modified) plants to meet the demand of sugarcane mills. Adoption of new technologies may help to overcome issues relevant to the stability, storage and overproduction of enzymes in plants. Sainz [91] reported that highly thermostable and hydrolytically efficient enzymes were produced by genetic engineering. Transgenic sugarcane plants overexpressing bacterial endoglucanase (EG) and fungal cellobiohydrolases (CBH I and CBH II) were developed. Targeting EG to chloroplasts and cellobiohydrolases to vacuoles resulted in elevated enzymatic activity in the mature plant leaves. This increased enzyme activity demonstrated that cellulose hydrolytic enzymes can be produced in sugarcane plants [92] and will boost up energy production from cane and its by-products including bagasse. In addition to the traditional agricultural products (food, feed and fiber), plants are emerging as a valuable source of energy, fuel, biomaterials and chemical precursors for the industry. Advancements in research are of pivotal importance to meet the increasing demand of quality raw materials [93]. Genetic engineering techniques are playing important role to achieve this goal and are envisioned to play leading role in the production and processing technology. For instance, input cost can be reduced by producing raw material in plants as plants have proved an effective platform for the production of industrially important compounds. GM microbes are commonly used at industrial scale for rapid conversion of raw materials into desired product. Conversely, a few GM crops have gained commercial status in spite of wide spread eagerness and renowned potential of genetic engineering for crop improvement [94]. Biotechnology occupies a central role in US Department of Energy (DOE) to develop crops with modified cell wall composition. The DOE has received encouraging appreciation because of their research on bioenergy crops and production of valuable processing enzymes by engineering metabolic and biochemical pathways [95]. To successfully attain national goal of bioeconomy, genetic engineering is appearing as a major contributor. A wide range of plants like corn, poplar, switchgrass, canola, sorghum, soybean (*Saccharum* L.) had been used to produce bioenergy but sugarcane is far better choice as is a perennial crop which does not require reseeding after each growing cycle. Hence, sugarcane is the most valuable crop for the production of bioethanol which can further be improved by employing biotechnological innovations.

are currently working to engineer sugarcane crop as a platform for large scale production of chemicals with industrial as well as therapeutic significance. Hence, Biotechnological interventions hold great promises to develop a better sugarcane crop with improved agronomic

Biotechnological Interventions for the Improvement of Sugarcane Crop and Sugar Production

http://dx.doi.org/10.5772/intechopen.71496

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Centre of Agricultural Biochemistry and Biotechnology (CABB), University of Agriculture

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Ghulam Mustafa\*, Faiz Ahmad Joyia, Sultana Anwar, Aqsa Parvaiz and

\*Address all correspondence to: drmustafa8@gmail.com

traits, sugar contents and biofuel production.

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**Author details**

Muhammad Sarwar Khan

Faisalabad, Pakistan

**References**
